1. Field of the Invention
The present invention relates to radios and global positioning system (GPS) receivers. More particularly, the invention relates to a combined GPS receiver and radio unit operable for sending and receiving GPS-derived location data and other information.
2. Description of the Prior Art
The global positioning system (GPS) is an electronic satellite navigation system which permits users to determine their position with respect to the Earth. Global positioning may be determined with a handheld GPS receiver which detects and decodes signals from a number of satellites orbiting the Earth. The signals from each of these satellites indicate the position of the satellite and the time at which the signals were sent. To decode the satellite signals, known as spread spectrum signals, and thereby calculate desired position and navigational data, a GPS receiver must first “find” or acquire the signals emitted from a minimum number of satellites. Once the receiver is “locked on” to the spread spectrum signals, the user's global position and other navigational data (e.g., velocity of movement) can be calculated.
In addition to the growing popularity and demand for GPS navigational devices, portable two-way radios continue to enjoy widespread popularity. In 1996, the Federal Communications Commission (FCC) established the Family Radio Service (FRS) so that families and other small groups could communicate with one another over very short distances (typically less than two miles) at no charge and without an FCC license. The FRS, which is one of the Citizens Band Radio Services, includes 14 channels in the UHF 465 MHz band. There are a number of commercially available two-way radios which are designed for use with the FRS.
The increasing use of both portable radios and GPS receivers has led to proposals to incorporate the two into combined units. It is anticipated that such combined units will provide enhanced capabilities such as the ability to transmit GPS-derived location data between two or more units so that the users of the units may monitor each other's location. For example, a family may use several of these combined units to not only communicate with one another but also to monitor each other's location so that parents may keep track of their children.
Unfortunately, currently-proposed combined GPS/radio units suffer from several limitations that limit their utility. For example, proposed designs provide no means for users to determine their distance from other radio users in their group or family. Such information is often useful, for example, so that parents may ensure that their children have not wandered too far off or so that hikers may accurately assess the distance between themselves and other hikers in their group.
Another limitation of currently-proposed combined GPS/radio units is that transmitted location data quickly becomes stale or outdated as the units move from place to place. This is a problem because a user may incorrectly rely upon previously-transmitted location data to determine the location of another user. For example, a parent may incorrectly assume that one of their children is in a particular location based on previously-transmitted location data and then later discover that the child has since wandered to a different location.
Another limitation of currently-proposed combined GPS/radio units is that, although they can display the location of other such units, they are not operable to display other useful location-type information for other units such as track logs and track back information. These types of information can be beneficial in search and rescue missions and other related applications.
Another limitation of currently-proposed combined GPS/radio units is that they provide no means for users to gather and transmit to other units location data for way points such as campsites, trail heads, and bodies of water. Instead, users who currently desire to display such way point location data must personally visit each way point to obtain its GPS-derived location.
Another limitation of currently-proposed combined GPS/radio units is that they permit the display of location data from one perspective only. This is a problem because it is often desirable to change the perspective or vantage point from which such information is viewed to compensate for movement of the units.
Another limitation of currently-proposed combined GPS/radio units is that users often unknowingly move beyond the communication range of the units and therefore lose communications. As mentioned above, the range of FRS radios is typically less than two miles, but many people often use FRS devices to communicate with others while hiking, skiing, boating, and other such activities where they may become separated by more than two miles. In an attempt to prevent loss of communications, many FRS radios have a signal strength indicator that provides an alert when its received signal strength begins to drop. Unfortunately, however, such indicators typically only provide such alerts after communications have already been lost or seriously degraded.
Accordingly, there is a need for an improved combined GPS/radio unit that overcomes the limitations of the prior art.